<span *ngIf="dataSource.length === 0">No data</span>

<table mat-table [dataSource]="dataSource" class="mat-elevation-z8">
  <ng-container matColumnDef="key">
    <td mat-cell *matCellDef="let element">{{ element.key }}</td>
  </ng-container>

  <ng-container matColumnDef="value">
    <td mat-cell *matCellDef="let element" class="select-all">
      {{ element.value }}
    </td>
  </ng-container>

  <tr mat-row *matRowDef="let row; columns: displayedColumns"></tr>
</table>
